This application claims the benefit of priority from Japanese Patent Applications Nos. 2001-082107 and 2001-083877, filed on Mar. 22, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a magnetoresistance effect device including first and second ferromagnetic material layers, whose magnetization directions change under an applied magnetic field, and a non-magnetic material layer inserted between the first and the second ferromagnetic material layers.
2. Discussion of the Background
A Tunnel MagnetoResistance or a Tunnel MagnetoResistive (TMR) device basically includes a three-layered film of a first ferromagnetic material layer, a dielectric material layer formed on the first ferromagnetic material layer, and a second ferromagnetic material layer formed on the dielectric material layer. A tunnel junction is formed and tunnel current flows between the first and the second ferromagnetic material layers via the dielectric material layer by applying voltage to both the ferromagnetic material layers. The tunnel junction""s electrical resistance changes in proportion to cosine of relative angle of magnetization directions of the first and the second ferromagnetic material layers. The junction resistance takes a minimum value when magnetizations of the first and the second ferromagnetic material layers are substantially in parallel and a maximum value when the magnetizations of the first and the second ferromagnetic material layers are substantially anti-parallel. Such a change in the resistance is referred to as a Tunnel MagnetoResistance (TMR) effect and the device utilizing the TMR effect is called a TMR device.
It is reported that the change in the resistance by the TMR effect is as large as 49.7% at room temperature (Appl. Phys. Lett. 77, 283 (2000)).
A TMR device can be used as a memory cell of a memory device, such as a magnetic random access memory (MRAM) of magnetic information.
One of the first and second ferromagnetic material layers may usually have a fixed or pinned magnetization in a predetermined direction and the fixed magnetization does not rotate/invert even when a magnetic field is applied. Another one of the first and second ferromagnetic material layers has a magnetization free to rotate/invert under the applied magnetic field, referred as a magnetization free layer. When the TMR device is applied to a memory device, such as the MRAM, the ferromagnetic material layer having the magnetization free to rotate/invert may also be referred to as a memory layer, because it retains in memory written magnetic information as a state of magnetization of the magnetization free layer, while the ferromagnetic material layer having a pinned magnetization may be referred as a reference layer.
By corresponding each state of parallel and anti-parallel directions of magnetization of the reference layer and the memory layer to the binary information of xe2x80x9c0xe2x80x9d or xe2x80x9c1,xe2x80x9d a TMR device can be used as the memory device.
Writing of the magnetic information can be achieved by providing an electrical current flow to a conductive line formed at a vicinity of the memory cell and inverting magnetization of the memory layer by a magnetic field generated by the electrical current.
The written magnetic information can be read by flowing tunnel current as a sense current to the TMR device and current detector or a voltage detector can sense the electrical resistance of the TMR device.
An integrated magnetic memory apparatus includes a number of memory cells each having the TMR device and a switching transistor, which is coupled to the respective TMR device of the same memory cell, and with a large number of memory cells aligned in a matrix. An arbitrary cell can be selected in known methods, for example, as employed in DRAM addressing. The integrated magnetic memory apparatus also includes bit lines extended in row directions and word lines extended in column directions. Each of the bit lines is coupled to a series of memory cells which are aligned in the same direction as the bit line extends. Each of the word lines is also coupled to a series of the memory cells aligned in the same direction as the word line extends. Peripheral circuits for controlling current or voltage of the bit and word lines are also provided at ends in row and column directions of the memory cell region.
A memory apparatus having the TMR devices and diodes in place of the switching transistors has also been reported (U.S. Pat. Nos. 5,640,343 and 5,650,958).
It is necessary to reduce the memory cell region for a highly integrated magnetic memory apparatus. Therefore, an area of ferromagnetic material layer is necessarily reduced, however, when the area of the ferromagnetic material layer is reduced, its coercive force increases. A magnitude of a switching magnetic field that is necessary for inversion of magnetization of the memory layer increases as the coercive force increases, and accordingly, a reduction in the plan area results to an increase in the switching magnetic field. In writing magnetic information, larger current flow is needed to write information with the increased switching magnetic filed, whereby power consumption of the apparatus increases. Therefore, the reduction in the coercive force of the memory layer is important in reducing the highly integrated magnetic memory apparatus into practice.
A multi-layered memory film is proposed in order to resolve the large power consumption. The multi-layered memory film including two ferromagnetic material layers and a nonmagnetic layer formed between the two ferromagnetic material layers, in which the two ferromagnetic material layers are antiferromagnetically coupled (Japanese Patent Laid-Open No. 9-251621, U.S. Pat. No. 5,953,248).
The two ferromagnetic material layers of multi-layered film differ from each other in magnetic moment or thickness. Directions of magnetization of the ferromagnetic material layers are in opposite directions by the antiferromagnetic interlayer coupling. Therefore, the magnetizations of the two ferromagnetic material layers are cancelled and the multi-layered film as a whole can be regarded as one ferromagnetic material layer having a small amount of magnetization.
When a magnetic field directed opposite to the direction of the magnetization of the multi-layered film is applied, magnetization of the two ferromagnetic material layers invert, while maintaining the antiferromagnetic coupling. In this case, its small coercive force determines a switching magnetic field of multi-layered film and inversion of magnetization can be carried out by a small amount of switching magnetic field. While having such advantage, the multi-layered film fabricated into a very small size for a highly integrated magnetic memory apparatus exhibits an effect of enlargement of xe2x80x9cedge magnetic domainxe2x80x9d such that a change in a magnetic structure pattern during magnetization inversion becomes complicated. As a result, the coercive force and the switching magnetic field increase. The edge domain appears as a magnetic structure, when a width of a short axis of small ferromagnetic material layer becomes about several micrometers to sub micrometer, at film end portions of a magnetic material layer owing to influence of a demagnetization field (J. App. Phys. 81, 5471 (1997)).
To prevent generation of edge domains, a method of fixing magnetization of the edge domain was proposed (U.S. Pat. No. 5,748,524, and Japanese Patent Laid-Open No. 2000-100153).
When magnetization of an edge domain is fixed, a behavior in magnetization inversion can be controlled. However, it becomes difficult to reduce the switching magnetic field. A new composition added to fix the magnetization for preventing the edge domains is not suitable for high-density integration.
A first object of the present invention is to provide a magnetoresistance effect device having a stable magnetization structure of a magnetic layer having a magnetization free to rotate/invert achieved by a simple device structure.
A second object of the embodiments of the present invention is to provide a magnetic memory apparatus, a portable terminal apparatus, a magnetoresistance effect head or a magnetoresistive head, and a magnetic reproducing apparatus or a magnetic recording and reproducing apparatus having the stable magnetization structure of a magnetic layer having the magnetization free to rotate/invert achieved by a simple device structure.
An third object of the present invention is to provide a magnetic memory apparatus, a portable terminal apparatus, such as personal digital assistant, a magnetoresistance effect head, and a magnetic reproducing apparatus including the magnetoresistance effect device.
According to a first aspect of the present invention, there is provided a magnetoresistance effect device including a first ferromagnetic material layer having a magnetization free to change in an applied magnetic field, a first nonmagnetic material coupling layer formed on the first ferromagnetic material layer, a second ferromagnetic material layer formed on the first nonmagnetic material layer and having a magnetization free to change in the applied magnetic field, a first nonmagnetic material spacer layer formed on the second ferromagnetic material layer, and a third ferromagnetic material layer formed on the first nonmagnetic material spacer layer and having a magnetization substantially fixed in the applied magnetic field. The first and the second ferromagnetic material layers are antiferromagnetically coupled at a magnetic coupling field J, where the magnetic coupling field J satisfies following equation, xe2x88x923 [kOe]xe2x89xa6J less than 0 [kOe].
According to a second aspect of the present invention, there is provided a magnetoresistance effect device including a first ferromagnetic material layer having a magnetization free to change in an applied magnetic field, a first nonmagnetic material coupling layer formed on the first ferromagnetic material layer, a second ferromagnetic material layer formed on the first nonmagnetic material layer and having a magnetization free to change in the applied magnetic field, a first nonmagnetic material spacer layer formed on the second ferromagnetic material layer; and a third ferromagnetic material layer formed on the first nonmagnetic material spacer layer and having a magnetization substantially fixed in the applied magnetic field, wherein the first and the second ferromagnetic material layers are ferromagnetically coupled.
In the first and the second aspects of the embodiments of the present invention, a magnitude J of magnetic coupling is synonymous to interlayer coupling magnetic field and the value can be calculated by Equation (1) shown below.
J=xe2x88x92Hsxc3x97Msxc3x97t/4xe2x80x83xe2x80x83(1) 
where Hs designates a saturated magnetic field (in Oe) of a magnetization free layer including the first and second ferromagnetic material layers and the nonmagnetic material coupling layer, Ms designates a saturated magnetization (in Oe) of the magnetization free layer and notation t designates a thickness (in nm) of the magnetization free layer. The saturated magnetic field Hs can be obtained by hysteresis of a magnetoresistance effect device. Values by the respective factors are provided by measuring materials and compositions of the first and the second ferromagnetic material layers and the nonmagnetic coupling layer from a cross-section of the device. Specification of the magnitude J of the magnetic coupling and the magnetic structure is not limited to these methods but can be specified also by other methods.
According to a third aspect of the present invention, there is provided a magnetoresistance effect device including a first ferromagnetic material layer including a center region of a first magnetization free to change in an applied magnetic field and edge regions of a second magnetization different from the first magnetization and being free to change in the applied magnetic field, a first nonmagnetic material coupling layer disposed on the first ferromagnetic material layer, a second ferromagnetic material layer disposed on the first nonmagnetic material coupling layer and including a center region of a third magnetization parallel to the first magnetization and free to change in the applied magnetic field and edge regions of a fourth magnetization different from the third magnetization and being free to rotate in the applied magnetic field, a first nonmagnetic material spacer layer formed on the second ferromagnetic material layer; and a third ferromagnetic material layer disposed on the first nonmagnetic material spacer layer and having a magnetization substantially fixed in an applied magnetic field.
In the third aspect of the present invention, the magnetic structure of the first and the third ferromagnetic material layers may be detected by MFM (magnetic force microscope) or a spin resolved SEM (scanning electron microscope) by exposing the first and the second ferromagnetic material layers.
According to a fourth aspect of the present invention, there is provided a magnetoresistance effect device including a first ferromagnetic material layer having a magnetization free to change in an applied magnetic field, a first nonmagnetic material coupling layer formed on the first ferromagnetic material layer, a second ferromagnetic material layer formed on the first nonmagnetic material layer and having a magnetization free to change in the applied magnetic field, a first nonmagnetic material spacer layer formed on the second ferromagnetic material layer, and a third ferromagnetic material layer formed on the first nonmagnetic material spacer layer and having a magnetization substantially fixed in the applied magnetic field. There is a roughness at an interface between the first ferromagnetic material layer and the first nonmagnetic material coupling layer or an interface between the second ferromagnetic material layer and the first nonmagnetic material coupling layer, and the roughness at the interface is more than 2 angstroms.
In the first through fourth aspects of the present invention, the third ferromagnetic material layer is a fixed magnetization layer in which the direction of magnetization substantially remains unchanged in an applied magnetic field, while the applied magnetic field can change the magnetizations of the first and the second ferromagnetic material layers.
According to the first through fourth aspects of the present invention, the switching magnetic field can be reduced. When invert magnetic field is applied to the magnetization free layers (first and second ferromagnetic material layers), the magnetization directions thereof are changed by the applied magnetic field. The applied magnetic field may be applied in parallel to or inclined to the direction of an easy magnetization axis of the magnetization free layers. The magnetization directions are inverted when magnetic coupling energy between the first and the second ferromagnetic material layers is reduced, therefore the switching magnetic field for switching the magnetization of the two layers can be reduced.
Further, the magnetization structure of the first and the second ferromagnetic material layers can be substantially symmetric with respect to a magnetic axis, and the magnetization structure differs from an apparatus characterized in non-symmetry magnetic structure disclosed in Japanese Patent Laid-Open No. 11-273337. As a result of the symmetrical structure, a reduction in magnetoresistance accompanied by magnetization inversion is relatively small, which is desirable for the magnetoresistance effect device.
According to a fifth aspect of the present invention, there is provided a magnetoresistance effect device including a magnetization free layer having a nonmagnetic material layer and ferromagnetic material portions, a nonmagnetic material spacer layer disposed on the magnetization free layer and a ferromagnetic material layer disposed on the nonmagnetic material spacer layer and having a magnetization substantially fixed in an applied magnetic field. The magnetization free layer has a magnetization free to change in the applied magnetic field and the ferromagnetic material portions are ferromagnetically coupled to each other.
According to a sixth aspect of the present invention, there is provided a magnetoresistance effect device including a magnetization free layer having a plurality of ferromagnetic material portions ferromagnetically coupled to each other and having a magnetization free to change in an applied magnetic field, a nonmagnetic material spacer layer disposed on the magnetization free layer; and a ferromagnetic material layer disposed on the nonmagnetic material spacer layer and having a magnetization substantially fixed in the applied magnetic field.
According to a seventh aspect of the present invention, there is provided a magnetoresistance effect device including a magnetization free layer having a nonmagnetic material layer and a first ferromagnetic material layer and having a magnetization free to change in an applied magnetic field, a nonmagnetic material spacer layer disposed on the magnetization free layer, and a second ferromagnetic material layer disposed on the nonmagnetic material spacer layer and having a magnetization substantially fixed in the applied magnetic field. The first ferromagnetic material layer has a non-uniform film thickness.
An integrated magnetic memory apparatus can be realized by providing a plurality of the same magnetoresistance effect devices mentioned above. The integrated magnetic memory may have a reduced switching magnetic field and may form a random accessible, non-volatile and low power consumption memory apparatus. A portable terminal apparatus, such as a portable telephone and a portable display apparatus provided with the magnetic memory apparatus is also useful. The magnetoresistance effect devices, mentioned above, can also be used in a magnetoresistance effect head. A magnetic reproducing apparatus provided with the magnetoresistance effect head is also useful.